Diseases of the cardiovascular system affect millions of people each year and are a leading cause of death throughout the world. The cost to society from such diseases is enormous both in terms of the number of lives lost as well as in terms of the costs associated with treating patients through traditional surgical techniques. A particularly prevalent form of cardiovascular disease is coronary artery disease (CAD), which is caused by atherosclerosis. Atherosclerosis is a disease in which the lumen (interior passage) of an artery becomes stenosed (narrowed) or even totally occluded (blocked) by an accumulation of fibrous, fatty, or calcified tissue (hereinafter referred to collectively for convenience as an occlusion). Over time, this tissue, known in medicine as an atheroma, hardens and occludes the artery. The partial stenosis or full occlusion of the coronary arteries that supply the heart muscle leads to ischemia (deficient blood flow) of the heart muscle, angina (chest pain), and can lead to infarction (heart attack) or patient death. Although drug therapies and modifications to diet and lifestyle show great promise for preventing and treating atherosclerotic vascular disease, many patients urgently require restoration of blood flow that has already been lost, especially in those having severely or totally occluded blood vessels.
In many cases, a patient suffering such a coronary vessel occlusion undergoes a coronary artery bypass graft (CABG) surgical procedure, more commonly known as a “heart bypass” operation to restore normal oxygenated blood flow to the heart muscle downstream of the occlusion. The heart bypass typically involves surgically attaching a blood vessel harvested from the patient's body from a source of oxygenated blood, e.g., the aorta or a site of the obstructed coronary artery proximal to the obstruction, to provide a conduit for oxygenated blood downstream or distal to the occlusion to restore the flow of oxygenated blood to the heart muscle. CABG surgery is generally lengthy, traumatic and subject to patient risk. Among the risk factors involved is the use of a cardiopulmonary bypass (CPB) circuit, also known as a “heart-lung machine”, to both pump blood and oxygenate the blood so that the patient's heart can be stopped or arrested during the surgery, with its function performed by the CPB circuit. Recently, beating heart procedures have been developed that eliminate the need for any form of CPB.
In one approach, the surgeon harvests a section of a blood vessel from the patient's venous or arterial system, closes any branching vessel openings, and prepares its proximal and distal ends to be attached in a “proximal anastomosis” and a “distal anastomosis” bypassing the occlusion. The proximal or inflow end of such a “free graft” can be attached via a proximal anastomosis at a site proximal or upstream to the occlusion or to another vessel supplying oxygenated blood, e.g., the aorta. Generally, a free graft is a section of the saphenous vein harvested from the patient's leg or segment of radial artery harvested from the patient's arm.
In another approach, an available blood vessel within the trunk is dissected from supporting tissue while leaving it connected to the source of oxygenated blood so as to provide a source vessel free end. The sites of excision of the “attached” graft are closed to avoid blood loss, and the source vessel free end is anastomosed to the obstructed coronary artery at a distal anastomosis site distally or downstream from the occlusion that obstructs or restricts blood flow.
The trunk hosts a number of potential grafts including, the left internal mammary artery (left IMA), the right internal mammary artery (right IMA), the radial arteries and three visceral arteries, one in the abdomen, and two in the lower abdominal wall, though the latter can be quite short and are generally of limited usefulness. The visceral arteries include the epigastric artery, the gastroepiploic artery and the splenic artery.
The left IMA is best used for bypass to the left anterior descending (LAD) coronary artery and its diagonal branches, whereas, the right IMA can be used for bypass to selected vessels more posterior such as the distal right coronary artery (RCA). The right IMA can also be used for bypass to selected marginal branches of the left circumflex coronary artery. A segment of radial artery harvested from an arm is generally used to revascularize the posterior surface of the heart. The right gastroepiploic artery can be used to revascularize almost any artery on the surface of the heart and is most commonly used for bypass to the distal RCA or the posterior descending coronary artery. In unusual circumstances, the splenic artery is used to revascularize posterior coronary arteries, but it is long enough to reach the marginal branches of the circumflex coronary artery.
Surgeons typically complete bypass grafts to the following coronary arteries in a patient undergoing multiple bypass surgery in roughly the following order: posterior descending coronary artery (PDA), RCA, obtuse marginal branch, circumflex coronary artery, diagonal branch, and LAD. More generally, surgeons typically revascularize the three coronary systems in the following order: right, circumflex, and anterior descending. However, the order can vary depending on whether the procedure is performed on a beating heart or an arrested heart. About three to four bypass grafts, of which one to three are free grafts, are generally performed per procedure when the heart is arrested. In contrast, about two to three bypass grafts, of which zero to two are free grafts, are generally performed per beating heart procedure. In general, one free graft is used per beating heart procedure.
Two anastomoses are performed when a saphenous vein or other blood vessel is used as a free graft in a CABG procedure; one to the diseased artery distal to the obstruction (outflow end) and one proximally to the blood vessel supplying the oxygenated blood (inflow end). End-to-side anastomotic techniques described further herein are usually performed, although end-to-end or side-to-side anastomotic techniques described further herein are performed at times. For example, sequential graft techniques or “jump” grafts which use side-to-side anastomoses can be used to conserve the amount of blood vessels required when more than one graft is required in any of the three coronary systems for complete revascularization of the heart.
The majority of surgeons will complete the distal anastomosis of a free graft prior to completion of the proximal anastomosis. The small percentage of surgeons who do complete the proximal anastomosis first usually do so to allow antegrade perfusion of cardioplegic solution through the graft during revascularization.
Construction of an anastomosis begins by first precisely locating the occlusion within the target coronary artery. Then, the anastomosis site(s) of the target coronary artery are isolated from the epicardial tissues and overlying fatty layers. Typically, blunt, rounded #15 scalpel blades are employed to dissect these tissues and layers away from the target coronary artery. Blood flow in the target coronary artery can be interrupted by, for example, temporary ligation or clamping of the artery proximal and distal of the anastomosis site. The target coronary artery wall is opened to form an arteriotomy, that is, an elongated incision at the anastomosis site extending parallel to the axis of the coronary vessel and equally spaced from the sides of the coronary artery that are still embedded in or against the epicardium. The arteriotomy is typically created by use of a very sharp, pointed, #11 scalpel blade to perforate the target coronary artery wall, and the puncture is elongated the requisite length using scissors. The length of the incision generally approximates the diameter of the graft or source vessel, e.g., a typical incision for a saphenous vein is about 4 to 5 mm. A “perfect arteriotomy” is an incision that has straight edges, that does not stray from the axial alignment and equal distance from the sides of the coronary artery, and is of the requisite length. A variety of techniques and devices may be used to form an arteriotomy and/or aortotomy, i.e., an incision in the aorta. For example, devices that can cut tissue may be used to form an incision in a vessel. Devices that can cut tissue include mechanical devices, e.g., scissors, scalpel, knife or punch, radio frequency (RF) devices, e.g., electrocautery devices, laser devices and ultrasound devices.
Next, it is necessary to prepare the attachment end or ends of the graft or source vessel by cutting the source vessel end to an appropriate angle for an end-to-side anastomosis or by closing the source vessel end and forming an elongated arteriotomy in the source vessel wall of a suitable length that is axially aligned with the source vessel axis for a side-to-side anastomosis. In an end-to-side anastomosis, it is necessary to prepare the attachment end of the source vessel by beveling its severed end typically at about 30 to 45 degrees. Generally, the surgeon uses surgical scalpels and scissors to shape the source vessel end or make the elongated arteriotomy slit in the source vessel, and sutures to close the open severed end. One method of forming an elongated arteriotomy of a suitable length axially aligned with the source vessel axis for a side-to-side anastomosis is shown, for example, in U.S. Pat. No. 5,893,369.
The prepared end or elongated arteriotomy slit of the bypass graft or source vessel is attached or anastomosed to the target coronary artery at the arteriotomy in a manner that prevents leakage of blood. The inner, endothelial layer, vessel linings are less thrombogenic than the outer epithelial layers. So, in one approach, the attachment of graft to target artery is made by everting and applying the interior linings of the bypass graft or source vessel and the target coronary artery against one another and suturing the everted linings together. Surgeons can construct the anastomosis via a ten-stitch running suture using 7-0 polypropylene suture material. The ten-stitch anastomosis typically comprises five stitches around the “heel” of the source vessel and five stitches around the “toe” of the source vessel. The five stitches around the heel of the graft comprise two stitches to one side of the apex of the graft and the artery, a stitch through the apex and two stitches placed at the opposite side of the apex. The graft is generally held apart from the coronary artery while the stitches are constructed using a needle manipulated by a forceps. Suture loops are drawn up and the suture pulled straight through to eliminate purse-string effect. The five stitches around the toe of the graft also comprise two stitches to one side of the apex of the graft and the artery, a stitch through the apex and two stitches placed at the opposite side of the apex. Again, suture loops are drawn up, the suture is pulled straight through to eliminate purse-string effect, and the suture ends are tied.
The proximal anastomosis of a saphenous vein free graft to the aorta, i.e., an aortosaphenous vein anastomosis, is formed by first removing the pericardial layer that covers the aorta. An occluding or side-biting clamp can be placed on the aorta at the anastomosis site. A small circular or elliptical portion of the ascending aorta is excised forming a small opening, or aortotomy, 4 to 5 mm in diameter. An aortic punch typically facilitates this procedure. The opening for a right-sided free graft is made anterior or to the right lateral side of the aorta, whereas an opening for a left-sided free graft is made to the left lateral side of the aorta. The opening is made proximal on the aorta if the free graft is to supply blood to the right coronary artery. If the free graft is to supply blood to the anterior descending coronary artery, the opening is made in the middle on the aorta. And, if the free graft is to supply blood to the circumflex artery, the opening is made distal on the aorta. The right graft opening is placed slightly in the right of the anterior midpoint of the aorta and the left graft opening slightly to the left. The end of the saphenous vein free graft is cut back longitudinally for a distance of approximately 1 cm. A vascular clamp is placed across the tip of the saphenous vein free graph to flatten it, thereby exposing the apex of the vein. Five suture loops of a running suture using 5-0 polypropylene are then placed around the heel of the saphenous vein free graft and passed through the aortic wall. Two stitches are placed on one side of the apex, the third stitch is placed precisely through the apex of the incision in the saphenous vein free graft, and the final two stitches are placed on the opposite side of the apex. Suture traction is used to help expose the edge of the aortic opening to ensure accurate needle placement. Stitches include about 3 to 5 mm of the aortic wall for adequate strength. Suture loops are then pulled up to approximate the vein graft to the aorta. The remaining stitches are placed in a cartwheel fashion around the aortic opening thereby completing the remainder of the anastomosis.
Left-sided grafts are oriented so the apex of the incision in the heel of the saphenous vein free graft will face directly to the left side. The stitches are placed in a clockwise fashion around the heel of the graft and in a counterclockwise fashion around the aortic opening. Right-sided grafts are oriented in a caudal fashion. The stitches are placed in a counterclockwise fashion around the heel of the graft and in a clockwise fashion around the aortic opening. Five suture loops complete the heel portion of the graft and an additional five or six are necessary to complete the toe of the graft. Finished proximal anastomoses tend to have a “cobra-head” appearance.
It is essential for the surgeon to take steps to minimize the possibility of thrombosis, narrowing and/or premature closure of the anastomosis due to technical errors. Some surgeons feel the proximal anastomosis must have a take-off angle of 45 degrees while other surgeons believe the take-off angle is not critical. In addition, it was felt that intima-to-intima contact of the vessels at the anastomosis was critical for endothelization to occur, thereby making an ideal union of the vessels. However, most surgeons now feel intima-to-adventitia contact is acceptable. The main objective of the surgeon is to create an anastomosis with an expected long-term patency rate of greater than 5 to 10 years. The creation of an anastomosis takes approximately 10-15 minutes.
Adequate exposure that affords acute visualization of the vessel walls is an essential requirement for creating a sutured anastomosis without error. Acute visualization of the vessel walls is mandatory in order to properly place each stitch and avoid inadvertently including the back wall of the vessel in a stitch, which in effect narrows or completely occludes the vessel. Most surgeons employ blood-less field devices such as shunts, snares, and misted blowers to achieve the required exposure.
Currently, manual suturing is the gold standard for creation of a vascular anastomosis. However, a number of cardiac surgical procedures, e.g., off-pump, beating heart CABG procedures, minimally invasive procedures and even totally endoscopic procedures with access through ports only, can require a variety of other anastomotic techniques. Avoiding the use of cross clamps and CPB or dramatically reducing pump run and cross clamp times can effectively minimize post-operative complications. For this reason, surgeons have been increasingly using easier, quicker, less damaging, but reliable automated, semi-automated, or at least facilitated methods to replace or enhance the normal process of a manually sutured vascular anastomosis.
The major objective of any CABG procedure is to perform a technically perfect anastomosis. However, creation of a technically perfect anastomosis is generally complex, tedious, time consuming and its success is highly dependent on a surgeon's skill level. Therefore, it is perceived that creation of vascular anastomoses without the need to perform delicate and intricate suture lines may enable surgeons to more quickly create simpler and effective anastomoses. Currently, a number of mechanical anastomotic devices, materials, techniques, and procedures are being developed for facilitating the process of forming an anastomosis including vascular clips or staplers, glues, adhesives or sealants, laser welding, mechanical couplers, stents and robot-assisted suturing. These techniques are being developed for performing end-to-end, end-to-side and/or side-to-side anastomoses with or without temporary blood flow interruption. In general, these techniques can include the use of various biomaterials and/or biocompatible agents. See, for example, U.S. Pat. Nos. 5,385,606, 5,695,504, 5,707,380, 5,972,017 and 5,976,178, and 6,231,565.
Sealants, adhesives or glues used in creation of vascular anastomoses are generally based on synthetic or biological substances or a combination of both that are used to either seal post-operative internal air or fluid leaks, or to close a topical wound. Surgical sealants are generally absorbable materials used primarily to control internal bleeding and to seal tissue. Surgical adhesives are stronger than sealants, are often non-absorbable, and typically are biologically based. Surgical glues are stronger than surgical adhesives, are often synthetic and non-absorbable, and are often used to close topical wounds. Surgical glues are typically made from cyanoacrylate adhesives that form strong tissue-to-tissue bonds and are used to bond a wide variety of materials. Biologically based sealants, adhesives or glues are generally derived from blood clotting components such as proteins (e.g., fibrinogen or fibrin), enzymes (e.g., thrombin) and/or platelets. Fibrin based sealants, adhesives or glues generally combine the protein fibrinogen with the enzyme thrombin to immediately begin the clotting process. One surgical adhesive currently being marketed includes a combination of collagen (proteins which form fibers to support body tissues), formalin (a form of formaldehyde), resorcinol and glutaraldehyde. Some sealants, adhesives or glues can be used to control bleeding or to reinforce suture or staple lines rather than to make tissues adhere, thus functioning more as hemostatic agents than glues.
There are a number of uses for sealants, adhesives or glues, such as replacement for sutures and staples in minimally invasive procedures, where the surgeon has little room to maneuver, or for the repair of aortic dissections, where the tissue is so thin it can be damaged by sutures. Such sealants, adhesives or glues can also be used for anastomotic sealing, in which the seal should not be absorbed, or carotid patching, where a complete seal is desired.
Laser welding techniques using laser energy emitted by CO2 lasers, argon lasers or Neodymium-YAG lasers, for example, which thermally join tissues together can also be used to create the anastomosis between the source vessel and coronary artery tissues. One possible mechanism of laser welding of tissues is the thermal denaturation and coagulation of collagen fibrils in the tissue, which generally occur above 60° C. Photosensitive dyes (e.g., indocyanine green) that absorb the laser energy can be applied to the tissues to be joined at the weld site to enhance the weld strength while minimizing thermal damage to the surrounding tissue. Photosensitive dyes used in laser welding procedures may or may not bind chemically to the tissue's proteins depending on their chemical structure. Laser welding can provide a watertight seal to hold bodily fluids in, thereby preventing blood loss, infections and repeat surgeries. Alternatively, a “solder” comprising synthetic and/or biological components that absorb the laser energy can be applied to the tissues to be joined at the weld site to enhance the weld strength while minimizing thermal damage to the surrounding tissue. For example, proteins such as albumin have been used in various solder formulations. Laser welding devices can include one or more flexible optical fibers and solder-delivery tubes that can be snaked through small ports or through a channel in an endoscope.
Mechanical anastomotic devices include stapling devices, clipping devices, ring and pin coupling devices, and suturing devices. These anastomotic devices can be automated or semi-automated. Mechanical anastomotic devices also include mechanical couplers including stents, ferrules, and/or rings. Materials used to form an anastomosis via a mechanical device and/or coupler must be biocompatible, bio-absorbable, bio-active and/or bio-inert.
One component intra-luminal mechanical coupling devices are generally stent-like in design. The graft and the target vessel, i.e., the aorta or coronary artery, are forced into tubular shapes by the device. In general, the application of this type of device is relatively easy. The device can be made to unfold by itself so no deformation forces are necessary at the anastomosis. In addition, angled anastomoses are possible. The device can however have a lot of foreign material exposed within the blood stream, thus increasing the risk of stenosis and thrombosis. In some cases, the device can prevent direct contact between the graft and the target vessel, thereby preventing the vessel walls from healing together. Intimal damage to both the graft and the target vessel can also occur during delivery of the device. Extra sealing methods, e.g., tissue sealants, may be necessary to provide a leak-free anastomosis. In addition, the size of the device is strongly related to the size of the vessels. Therefore, a range of devices and measurement of the vessels is necessary.
Two component intra-luminal mechanical coupling devices require both the graft and the target vessel to be connected to their own coupling component, after which the two coupling components are connected to each other, thereby forming the complete anastomosis. Problems associated with construction of an anastomosis using a two component intra-luminal mechanical coupling device can include mounting of the vessels and connection of the components. Tools for mounting the individual coupling components to each vessel and tools for connecting the coupling components together are both generally required.
One component, extra-luminal, mechanical coupling devices typically allow direct intima-to-intima contact and typically require a delivery tool to position the coupling device in the recipient vessel. In addition, this type of device present less foreign material in the blood stream, thereby decreasing the risk of stenosis and thrombosis. However, mounting of the graft to the coupling device may not be easy. Damage can occur to the intimal layer when everting the graft onto the device for two reasons: 1) one tip of a pair of pincers used to solidly grab vessel wall to evert an artery will roughly touch and pinch the intima of the artery; and, 2) eversion causes high strain (stretching) that can damage the arterial wall. A high level of surgical skill and experience is necessary to reduce the probability that such damage occurs. The skilled surgeon must estimate where to grab the vessel wall and how to evert the graft onto the device to obtain a symmetrical anastomosis. A specially designed mounting tool can make the step of mounting the graft onto the coupling device easier and can help to minimize damage to the graft. In addition, care must be taken to avoid compression of tissue by the coupling device since compression can cause pressure necrosis.
Two component extra-luminal mechanical coupling devices, like the two component intra-luminal mechanical coupling devices, require both the graft and the target vessel to be connected to their own coupling component, after which the two coupling components are connected to each other, thereby forming the complete anastomosis. Problems associated with construction of an anastomosis using a two component extra-luminal mechanical coupling device also include mounting of the vessels and connection of the components. Tools for mounting the individual coupling components to each vessel and tools for connecting the coupling components together are both generally required. Hybrid anastomosis techniques combine one or more techniques, e.g., sutures or clips with glues or laser welding. A specific example of a hybrid anastomotic technique is the use of an intraluminal stent-like device combined with an extraluminal application of biological glue.
Various types of artificial biocompatible reinforcement sleeves or rings, e.g., those shown in the above-referenced '369 patent can be used in the anastomosis. Other examples of forming the arteriotomy, the shaped end or side wall of the source vessel, and the positioning and attachment of the source vessel and target artery together are set forth in U.S. Pat. Nos. 5,799,661, 5,868,770, 6,026,814, 6,071,295, 6,248,117, and 6,332,468.
Largely invasive surgical techniques are typically employed to provide the surgeon access to the anastomoses sites. For this reason, CABG surgery is generally performed through a median sternotomy (open-chest surgical exposure). A median sternotomy incision begins just below the sternal notch and extends slightly below the xyphoid process. A sternal retractor is used to separate the sternal edges for optimal exposure of the heart. Hemostasis of the sternal edges is typically obtained using electrocautery with a ball-tip electrode and a thin layer of bone wax.
Typically, fat layers that make it difficult to see either the artery or the occlusion cover the epicardial surface and the obstructed cardiac artery. However, surgeons are able to dissect the fat away to expose the artery and manually palpate the heart to feel the relatively stiff or rigid occlusion within the artery as a result of their training and experience. The surgeon can determine the location and length of the occlusion as well as suitable sites of the target coronary artery for the proximal and distal anastomoses with some degree of success. However, it is difficult to accurately determine the bounds of a soft or “cheesy” occlusion, and mistakes can happen.
The open chest procedure involves making a 20 to 25 cm incision in the chest of the patient, severing the sternum and cutting and peeling back various layers of tissue in order to give access to the heart and arterial sources. As a result, these operations typically require large numbers of sutures or staples to close the incision and 5 to 10 wire hooks to keep the severed sternum together. Such surgery often carries additional complications such as instability of the sternum, post-operative bleeding, and mediastinal infection. The thoracic muscle and ribs are also severely traumatized, and the healing process results in an unattractive scar. Post-operatively, most patients endure significant pain and must forego work or strenuous activity for a long recovery period.
Many minimally invasive surgical techniques and devices have been introduced in order to reduce the risk of morbidity, expense, trauma, patient mortality, infection, and other complications associated with open-chest cardiac surgery. Less traumatic limited open chest techniques using an abdominal (sub-xyphoid) approach or, alternatively, a “Chamberlain” incision (an approximately 8 cm incision at the sternocostal junction), have been developed to lessen the operating area and the associated complications. In recent years, a growing number of surgeons have begun performing CABG procedures using minimally invasive direct coronary artery bypass grafting (MIDCAB) surgical techniques and devices. Using the MIDCAB method, the heart typically is accessed through a mini-thoracotomy (e.g., a 6 to 8 cm incision between a patient's ribs or intercostal space) that avoids the sternal splitting incision of conventional cardiac surgery. A MIDCAB technique for performing a CABG procedure is described in U.S. Pat. No. 5,875,782, for example.
Other minimally invasive, percutaneous, coronary surgical procedures have been advanced that employ multiple small trans-thoracic incisions to and through the pericardium, instruments advanced through ports inserted in the incisions, and a thoracoscope to view the accessed cardiac site while the procedure is performed as shown, for example, in the above-referenced '468 patent and in U.S. Pat. Nos. 5,464,447, and 5,716,392. Surgical trocars having a diameter of about 3 mm to 15 mm are fitted into lumens of tubular trocar sleeves, cannulae or ports, and the assemblies are inserted into skin incisions. The trocar tip is advanced to puncture the abdomen or chest to reach the pericardium, and the trocar is then withdrawn leaving the port in place. Surgical instruments and other devices such as fiber optic thoracoscopes can be inserted into the body cavity through the port lumens. As stated in the '468 patent, instruments advanced through trocars can include electrosurgical tools, graspers, forceps, scalpels, electrocauteries, clip appliers, scissors, etc.
In such procedures, the surgeon can stop the heart by utilizing a series of internal catheters to stop blood flow through the aorta and to administer cardioplegia solution. The endoscopic approach utilizes groin cannulation to establish CPB and an intraaortic balloon catheter that functions as an internal aortic clamp by means of an expandable balloon at its distal end used to occlude blood flow in the ascending aorta. A full description of an example of one preferred endoscopic technique is found in U.S. Pat. No. 5,452,733, for example.
However, recently developed, beating heart procedures eliminate the need for any form of CPB, the extensive surgical procedures necessary to connect the patient to a CPB machine, and to stop the heart. These beating heart procedures can be performed on a heart exposed in a full or limited thoracotomy or accessed percutaneously.
In such percutaneous procedures, the epicardium of the beating or stopped heart is exposed for viewing typically by use of grasping and cutting instruments inserted through a port to cut through the pericardium surrounding the heart while the area is viewed through a thoracoscope or endoscope, e.g., inserted through a different port. Once the heart is exposed, it is necessary to locate the target coronary artery as well as the occlusion. In this case, it is not possible for the physician to manually palpate the fatty tissue overlying the artery and occlusion to accomplish this.
Fluoroscopy is widely employed during coronary catheterization to provide a real-time X-ray image to visualize the position of devices advanced within the vascular system of a patient. Bi-plane fluoroscopy, provides two real-time x-ray images acquired from different angles to visualize a totally occluded coronary artery. However, biplane fluoroscopy is costly and slow, and erroneous interpretation of the images often occurs.
A reliable technique is needed for precisely determining the relative positions of a therapeutic working device, the boundaries of an occlusion, and the structure of the occluded artery as the working device is manipulated or otherwise. Therefore, it has been proposed to employ instruments, e.g. catheters and guidewires, that can be advanced either through the artery lumen and the occlusion in the target coronary artery itself or via a percutaneous port lumen, or both, to identify suitable unobstructed sites of the target coronary artery for proximal and/or distal anastomoses.
A hand held probe is disclosed in U.S. Pat. No. 6,248,072 that is adapted to be advanced against the epicardium by the surgeon to determine the location of the target coronary artery and the occlusion within the arterial lumen. The probe incorporates an ultrasound transducer at the probe end in contact with the heart that emits and receives reflected ultrasound signals. The reflected ultrasound signals are processed in external equipment to develop images indicative of the tissue that the transducer is applied to by the physician. It is implied that unobstructed anastomosis sites can be determined by the characteristic display of an ultrasound image of an open arterial lumen. The physician may mistakenly locate and open the wrong vasculature lumen unless the physician knows approximately where the target coronary artery resides, because the probe only identifies lumens from cardiac tissue. In fact, it can be difficult to distinguish between a lumen of an artery and that of a vein. Smaller vessel diameters can also be harder to identify than larger diameter vessels. It appears the probe would be unable to precisely identify the targeted coronary artery. Further, in a closed-chest procedure, it can sometimes be very difficult to identify a specific area of the heart while viewing the heart with an endoscope having a limited field of view thereby making it difficult to precisely locate the targeted vessel.
The use of intravascular ultrasound catheters having distally disposed ultrasonic transducers is disclosed in U.S. Pat. No. 6,026,814. The '814 patent relates to systems for performing CABG almost entirely employing intravascular catheters and devices. In one embodiment of the '814 patent, a first ultrasound catheter is advanced from a surgically created opening in a peripheral artery, e.g., the femoral artery, to and through the occlusion in the target coronary artery to a distal anastomosis site. A second ultrasound catheter is advanced in a similar fashion into the lumen of the source vessel to locate a further ultrasound transducer at the site where the source vessel is to be anastomosed to the distal anastomosis site of the cardiac artery. The ultrasound transducers act as transmitters and receivers in order to guide the distal end of the source vessel to the distal anastomosis site. Instruments that are advanced through the source vessel are used to perform the arteriotomy in the target coronary artery at the distal anastomosis site and to anastomose the target coronary artery to the source vessel. According to the '814 patent, one of the ultrasound transducers is positioned in the lumen of the source vessel while the other is positioned in the target vessel. Therefore, the size of the vessels, i.e. the diameter of the vessels, will dictate the size or diameter of the ultrasound transducers or other types of transmitters and receivers. The '814 patent does suggest that a number of other cooperating transmitters and receivers, e.g., RF signal transmitter and receiver, one or more point light source and photodiode, electromagnet and magnetic field responsive element can be substituted for the ultrasound transmitter and receiver. However, these transmitters and receivers will be limited in size required to fit in a source vessel or a target vessel. The smaller size may limit the effectiveness of the transmitters and receivers. For example, the size of an ultrasound transducer can limit the distance and resolution that images may be acquired. Further, the length of the source vessel must be determined prior to guiding of the distal end of the source vessel to the distal anastomosis site. Therefore, the physician would need to know the exact length the source vessel must be prior to guiding of the vessel. If the physician chooses the wrong length, the source vessel may end up to short or to long, both of which may be detrimental to the creation of the anastomosis. In addition, it may be very difficult to manipulate and guide the source vessel having an ultrasound transducer inside itself to the target vessel.
The use of a hand held ultrasound instrument and system to pass a relatively stiff distal segment guidewire through a hardened obstruction that cannot be crossed by the typical soft tip guidewire is disclosed in U.S. Pat. No. 6,241,667. Typically, a guidewire is advanced from a surgically created opening in a peripheral artery, e.g., the femoral artery, to the occlusion in the target coronary artery and the guidewire (or a catheter advanced over the guidewire) is advanced through the occlusion. This approach of placing a variety of devices for performing procedures in the arterial system, e.g., at the occlusion, is well known in the field of interventional cardiology. The guidewire is maneuvered into place to act as a guide for positioning the placement of catheters or devices “over the wire.” The guidewire outer diameter typically ranges from 0.010 to 0.038 inches whereas an interventional catheter lumen diameter typically ranges from 0.040 to 0.25 inches so that a combination of guidewire and interventional catheter can be selected that suits the vascular lumens of a particular vascular pathway.
In one embodiment of the '667 patent, an imaging locator comprising an imaging tube and an ultrasonic transducer is passed through an incision in the chest of a patient and positioned adjacent the surface of the heart and outside an occluded coronary artery. A catheter having a tissue-penetrating working element is disposed in the catheter delivery lumen of the imaging tube. During operation, the working element is advanced from the catheter delivery lumen and steered and manipulated through the arterial wall distal to the occlusion and advanced proximally to cross the occlusion retrograde while being imaged by the imaging locator. A guide catheter is then advanced from a surgically created opening in a peripheral artery, e.g., the femoral artery, to the proximal or upstream side of the occlusion in the target coronary artery. The working element is then advanced into the lumen of the guide catheter until it can be grasped outside the body, whereupon the guide catheter is removed.
Again, the physician may mistakenly locate and open the wrong vasculature lumen unless the physician knows approximately where the target coronary artery resides, and it may be difficult to distinguish between a lumen of an artery and that of a vein. Smaller diameter vessels may also be harder to identify than larger diameter vessels. Therefore, the imaging locator alone may be unable to precisely identify the targeted coronary artery. Furthermore, in a closed-chest procedure it can sometimes be very difficult to identify a specific area of the heart while viewing the heart with an endoscope having a limited field of view thereby making it difficult to precisely locate the targeted vessel.
U.S. Pat. Nos. 5,722,426, 6,080,175 and 6,113,588 disclose the use of light emission to assist in locating an occlusion in a target coronary artery by illuminating the arterial lumen with light that the surgeon can observe through a thoracoscope or directly when the epicardial surface is exposed to view in a thoracotomy. A hand held probe is disclosed in the '426 patent that is adapted to be inserted through an incision made in the target coronary artery upstream or downstream from the occlusion and advanced toward the occlusion to determine its respective upstream or downstream end. The probe incorporates a plurality of light sources along the probe end that emit light as the probe is advanced. It is asserted that the light can be seen through the vessel wall and that the light brightness is attenuated as the probe penetrates the occlusion. Unobstructed anastomosis sites can be determined by viewing the change in light brightness. Catheter borne light emitters are disclosed in the '175 and '588 patents. Again a catheter is advanced from a surgically created opening in a peripheral artery, e.g., the femoral artery, to and through the occlusion in the target coronary artery to a distal anastomosis site. The light transmitted through the arterial wall is observed, and it is asserted that unobstructed anastomosis sites can be determined by viewing the change in light brightness.
However, the ability of a surgeon to visually ascertain changes in light brightness of a light shining through a vessel wall either directly or through a thoracoscope can be hampered if the light is diffused in the tissue of the vessel wall or is blocked by an obstruction or any fatty tissue overlying the blood vessel and epicardium. The thickness of cardiac tissue and fatty deposits located between the coronary artery and the surface of the heart can vary greatly among patients. This variance in tissue thickness and fatty deposits can effective a surgeon's ability to accurately identify unobstructed anastomosis sites, since the surgeon's ability to visually ascertain changes in light brightness shining through a vessel wall can be diminished. Moreover, environmental conditions of the operating room, particularly the brightness of the room or the surgical field, can diminish the brightness of the transmitted light and make it difficult to see.
A further probe, referred to as the “H-Probe”, is described by Verimetra, Inc. at www.verimetra.com/MEMS_Sensors_for_Surgery/H-Probe/h-prove.html. The H-Probe is described as a MEMS-based instrument designed to palpate vessels to determine the position of internal plaque. It is asserted that the MEMS-based vessel hardness H-Probe at the end of an MIS tool will minimize, if not eliminate, erroneous choices for bypass procedure location, leading to reduced post-operative complications.
While these approaches may hold promise, in some instances they are either unduly complicated to practice or not specific enough. Simple devices and methods that can positively identify vessels and suitable anastomosis sites with high specificity remain highly desirable. Such devices and methods would be useful in locating or tracking body vessels exposed in a surgical field but obstructed by overlying tissues.